1. Field of the Invention
This invention relates to the tape reel of a magnetic recording tape cassette used for the recording and read-out of image information and the like. More particularly, this invention relates to double injection molding of an inexpensive tape reel using two types of resin.
2. Description of the Prior Art
As shown by the cutaway drawing of FIG. 10 and the longitudinal cross-section view of FIG. 11, a magnetic tape recording cassette consists of an upper case 1 and lower case 2, each of which is a flat, rectangular parallelopiped, and which are fixed together, with two reels 3, 4 rotatably housed therein. Conventionally the reel has consisted of an upper flange 5 formed from clear AS resin, and a reel lower portion 12 consisting of a hub 6, shaft hole wall 7, shaft hole bottom wall 8, connecting ribs 9, lower flange 10 and protruding shaft 11 integrally formed of wear-resistant POM resin, the upper flange 5 being affixed to the shaft hole bottom wall 8 on the opposite side to the shaft hole 13 formed by the shaft hole wall 7 and the shaft hole bottom wall 8. The protruding shaft 11 is in constant contact with a metal, strip-shaped reel restraining spring 14 which presses on the protruding shaft 11 with a force of 100-200 g when the cassette has been loaded into the recording/read-out apparatus, and it is because during the course of recording or read-out using the entire length of the tape the reels rotate some 1,500 times that the protruding shaft 11 is made from wear-resistant POM resin.
Because the protruding shaft 11 is made of POM resin, the same resin must be used for the entire reel lower portion 12 which is formed integrally with said protruding shaft 11; the cost of POM resin being high compared with a general-purpose resin such as ABS resin or the like, this has tended to increase the cost of the reels. In an attempt to solve this problem, there has been proposed a method whereby POM resin is used to form only the protruding shaft 11, with the other parts of the reel lower portion 12 being formed of ABS resin, and the protruding shaft 11 is affixed between the upper flange 5 and the shaft hole bottom wall 8 formed integrally with the reel lower portion 12. However, the problem with this method was that it involved more parts and more assembly operations, so it did not result in a cost reduction.